Variable condenser



Dec. l5, 1931. H. rV ELLIOTT VARIABLE CONDENSER Filed Aug. 25, 1925 2Sheets-Sheet l "hm" K HHH /6 /5 Z7 Z5 j \J0 /z x J7 -v- A "v 6 W4 @i E A4 /3 :E

// fg, Z 60 lNvENToR Haro/d E EMO/ BY fat HIS ATTORNEY Dec. 15, 1931. H.F. ELLIOTT VARIABLE CONDENSER Filed Aug. 25, 1925 2 Sheets-Sheet 2INVENTOR Hara/d E f//nff @Y 4W HIS ATTORNEY timeafter the condenser isin use.

Patented Dec. 15, 193i N i 'r TTE HAROLD F. ELLIOTT, 0F lPAL() ALTO,CALIFORNIA, ASSIGNOR, BYIMESNE ASSIGNMENTS, TO RADIO CORPORATION OFAMERICA, 0F NEW YORK, N. Y., .A CORPORATION OF DELAWARE VARIABLE CON DENSER.

Application ledAugust 25, 1925. Serial No. 52,384.

This invention relates to an apparatus for varying the capacity of anelectric circuit, and especially to a condenser having relativelymovable electrodes.

Such devices are now lin common use 1n connection with systems for radiotransmission and reception. The recent extensive development inbroadcasting has especially created a large demand for simple andinexpensive instruments for tuning high frequency circuits, so essentialto secure selectivity in a receiver set. The most common form of such acondenser includes a plurality` of interleaving flatplates of conductingmaterial, formed into two sets. The extent of the interleaving can bevaried in orderto vary the capacity between the sets of plates. The flatVplates in such condensers must be carefully assembled, and adjustedafter assembly in orderto assure proper interleaving without shortcircuits; and such adjustment of the plates is usuallya'equired fromtime to Furthermore, the contact between the individual plates and thecommon support for each set, is apt to 'become loose, with attendantloss in efficiency and sharpness.

Other forms "of variable condensers also have structuural disadvantages.It is one of the objects of my invention to obviate substantially allsuch disadvantages, 'and' to make it possible to construct a simple andreliable variable condenser that can not O 'nly be manufactured at a lowcost, but assembled easily and kept in good Working order indefinitely.

It is another object'ofmy invention .to obviate the necessit foraccurateadjustments of any'of 'the moving parts duringjassembly.

In and near substantially all of the large cities, there are now anumber of broadcasting`r stations from which radio signals lcan easilybe received. :,In order to impart selectively, it is -desirablethatthevariable'com' Adenser be adjusted by a substantial amount in vary-ing"the frequency of resonance of'iltsVx associated ,radio circuit, from thefrequency of one station to that ofA the station broadcasting at thenearest frequency to that of the first. In other words, it is desirableto have a variable condenser for tuning la circuit, by which thestations are separated b'y an appreciable condenser adjustment. Sincebroadcasting stations are numerous and operate within a limited range offrequencies (approximately from 500,000 cycles to 1,500,000 cycles), theseparation of the stations in this manner is sometimes diiiicult. It isthus another object of my invention t0 make is possible to tune areceiver circuit in such a Way vthat the frequencies of operation areseparated to a substantial extent in the variation of the condenser.

In order to secure the foregoing advantage,

I arrange the relative movement of electrodes 35 in such a way that theamount of the movement is directly proportional to the difference in theresonant frequency of the circuit being tuned. In this Way, thecharacteristic curve of the condenser, connecting the settin of thecondenser withjthe frequency at W ich the particular setting provides atuned circuit, is a straight line, when plotted in rectangularcoordinates.

It is still another object of my invention to make it lpossible to varythe capacity of the condenser by minute increments in a convenientmanner. Ordinarily, variable condensers are adjustable by the aid ofalrotatable shaft, and in accordancewith my invention, 30

the extent of angular movement of the shaft can be made as large asdesired, tosecure accurate adjustment of the condenser.

It is another object of my invention to provide a reduction mechanismfor this large 35 angular movement, whereby itis possible -t-o indicatethe variation of the condenser l"by the aid of a single dial of theordinary form.

It is' another object of my invention to` make it possible'to operate aplurality of B0 vnusparts of condensers n-acemm'ercil'waiy 95 v and on alarge scale, and yetfiisure thatfa of the parts can be readily fittedand assembled together to form a simple and rugged structure.

My invention possesses many other advan- 109 tages, and has otherobjects which may be made more easily apparent from a consideration ofseveral embodiments of my invention. For this purpose I have .shown afew forms in the drawings accompanying" and forming part of the presentspecification. I shall now proceed to describe these forms in detail,which illustrate the general principles of my invention; but it is to beunderstood that this detailed description is not to be taken in alimiting sense, since the scope of my invention is best defined by theappended claims.

Referring to the drawings:

Figure 1 is a sectional view of a variable condenser constructed inaccordance with my invention;

Fig. 2 is a fragmentary view of a modified form of the condenser,illustrating especially the manner in which the large angular movementof the condenser shaft may be reduced, for securing proper indications;

Fig. 3 illustrates a. further embodiment of my invention, and discloseshow several variable condenser elements can be arranged to be operatedin unison;

Fig. 4 is a sectional View of a further modification; and

Fig. 5 is a curve showing the relation between the dial setting and thefrequency of resonance of the circuit with which the variable condenserconstructed in accordance with my invention is associated.

In Fig. l, I illustrate a variable condenser adapted to be mounted on avertically arranged panel 11. As is common, a rotary dial 12 is arrangedon one side of the panel for manual control, and the condenser parts arearranged on the other side of the panel to be hidden from View. Theactive portions of the condenser include a pair of electrodes which maybe moved relatively to each other by manual rotation of the dial 12. Oneof the important features of my invention resides in the form of theseelectrodes. They are arranged in such manner that upon relativemovement, there is a Variation in the active surfaces of-the,electrodes, as well as of the thickness of the dielectric betweenthem.

This I can accomplish by arranging the electrode'surfaces obliquely tothe direction of their relative movement. A convenient manner in whichthis may be accomplished is by forming one metal electrode, such as 13as a portion of an internal cone surface, and by forming the otherelectrode 14 with a cooperating external cone surface, there being` amovement of one electrode with respect to the other along thecommon axisof the cone surfaces, which are thus concentrcally formed. In order tofacilitate the mounting of the electrodes and to provide for properaxial movement, the electrode '13 has a disclike'portion 15 with acentral hub 1G projectnegates ing toward the other electrode. A lefthand hub 17 is threaded, and is arranged to`project thru an aperture inthe panel 11. A washer 18 and a nut 19 are passed respectively over thefree end of this hub 17 in order to clamp the electrode 13 securely onthe panel 1l.

'The right hand hub 16 forms a convenient guide upon which the otherelectrode structure can slide. In order to accomplish this result, theelectrode 14 is supported on the outer face of a cone shaped disc 2Omade from appropriate insulation material such as bakelite. Theelectrode 14 forms a covering for the periphery of this disc 20; and italso has depending portion 21 inset in its left hand ace.

It is evident that telescopic or axial movement of disc 20 on hub 16will serve to vary the spacing of the active surfaces of the twoelectrodes. The rate of the variation can be very accurately determinedby proper choice of the cone angle a. It is further evident that theaxial movement being oblique with respect to the active surfaces, thethickness of the dielectric between the surfaces is varied by suchmovement as Well as the area of the active surfaces.

Due to the concentric arrangement, it is possible to manufacture theelectrode structures 13 and 14 on a commercial scale with sufficientaccuracy to insure proper centering of one with respect to the other.There is no necessity of further adjustment after assembling, for themere act of assembling is sufficient to space the electrodes properlywith respect to each other.

The electrode 13 can be provided with a binding post structure 22fastened in this instance, near the upper portion of the concentricactive surface of this electrode.

In order to slide the disc 20 on the hub structure 16, any appropriatemechanical movement may be used. In the embodiment of Fig. 1 Iillustrate a worm 23 mounted-on a 'shaft 24 that is rotatable Within thehubs 16 and 17. This Worm is fastened to the right hand end of shaft 24by the aid of the screw threads 25. In order to provide for relativeaxial adjustment of the Worm with respect to the shaft 24, the end ofthis shaft where it is threaded is split, and a wedge in the shape of ascrew 26 is provided in the end of the shaft to spread this end of theshaft and to clamp it-tight to the worm 23. By the aid of thisstructure, it is possibleto adjust the relative axial positions of theworm 23 and the shaft 24. The disc 20 has a hub 27 provided with a nutportion 28 in which the worm 23 engages. It is evident that on rotationof shaft 24 the hub 27 will be moved axially, provided this hub isrestrained from rotation. The rotation of shaft 24 is accomplished bythe aid of the dial 12, which is fastened to the extension 29 of theshaft 24. Restraint against rotation of disc 2() is accomplished by theaid of a member 30 in the form of a flat spring, apertured to permitpassage of hub 27. `One end of the spring is fastened as by a rivet 31to the disc 20, and theother end is fastened by the aid of a bindingpost structure 32 to a casing 33 of insulating material. The flat spring30 may thus serve as the lead-in con nection for the electrode 14 by theaid of the rivet 31, which extends thru the disc structure 20 andelectrically connects the spring 30 with the depending portion 21 of theelectrode 14. The spring also serves conveniently to hold the nut 27frictionally against the worm 23, whereby said worm is maintainedagainst inadvertent movement. The cover 33 is arranged to telescope overthe projection 33 of the electrode 13 and may be fastened thereto by theaid of a series of screws 34. Thus a dust proof casino,r is provided forall of the moving parts of the condenser.

The binding post structure 32 extends thru the cover whereby connectionmay be made to it externally of the enclosed structure.

The mode of operation of the device is evident from the foregoingdescription. When assembling the parts, the movable electrode structure14-20 is properly alined without the necessity of frequent or furtheradjustments. Furthermore, it should be noted that as the disc 20 movesto the left axially on the hub 16, the extent of the surfaces which areactive on the two electrodes becomes greater and greater, while at thesame time, the dielectric thickness between them is reduced. The wallsof the enclosing casing may conveniently form stops, limiting themovement of the electrode structure 20. By the aid of the wedge screw26, it is possible to adjust the axial position of the worm 23 withrespect to the hub 16, to avoid end play. The axial position of theelectrode 20 may then be adjusted and the dial 12 set to give thedesired reading. In this way, it is possible to adjust the dial readingto compensate for minor electrical effects.

It is also to be noted that since both electrodes are rigidly supportedon parts capable of being finished accurately in large quantities, theprocess of assembly is rendered extremely simple. tSince the amount ofdielectric between the electrodes is small, there is a minimumdielectric loss. Furthermore, the worm and nut construction can be sodesigned that the dial 12 can be made to vary the electrode spacing t aslow rate, whereby accurate adjustment ie afforded.

A further very important advantage is that. by ycalculation and onactual trial. it has been found that a condenser constructed inaccordance with this disclosure varies` the frequency of resonancesubstantially as a straight line function with respect to the dial,order to obviate this difficulty,

setting. Thus, in Fig. 5, there is reproduced a curve in which theabscissae are dial settings, reading from 0 to 200 and corresponding tocomplete movement of the disc 20, and the ordinates representfrequencies in kilocycles corresponding to the frequency of resonancefor the particular dial settings represented by ,the abscissae. Thiscurve represents an actual test taken With the apparatus, and has markedthereon the various broadcasting stations which were tuned in by the aidof the condenser. It is seen that they fall substantially on a straightline. This is a highly desirable feature, for the stations can be keptseparated and the arrangement is selective.

It is evident that in the construction of yF'g. 1, the dial 12 mustrotate thru several revolutions in order to produce a full movement ofthe disc 20. Under such circumstances, it is not practicable to keeptrack of the angle of movement of the shaft 24. In

modification in Fig. 2 in which this dial movement is reduced by the aidof a reduction mechanism such as planetary gears arranged in a compacttrain. In this figure, the shaft 24 is mounted for rotation as before ina hub 35 of the stationary electrode 13. The knob 36 is securelyfastened to the shaft at its free extremity, and is arranged to impart areduced motion to the dial 37, coacting with a stationary index plate38. This dial is free to rotate on shaft extension 29. This index plateis fastened by the lock nut 39 to the panel 11, which lock nut servesalso to hold the stationary electrode 13 in place.

In order to provide a reduced motion to the dial 37, a small gear 4() isfastened on the shaft 24 and is arranged to mesh with and drive one ormore planetary gears 41. These planetary gears are rotatably mounted onshort stub shafts 42 fastened on the inner side of the dial 37, and meshwith a stationary gear 43 formed on an internal surface of the Hange 44,integral with the index plate 38. It can readily be proven thatbylmaking pinion 4()V small enough, and the diameter of the internalgear 43 large enough, any desired reduction in the movement of the dial37 can be obtained. Thus, movement of gear 40, due to movement of knob36, results partly in a rotary movement of planetary gears 41 abouttheir own axes, and partly in a planetary movement; the planetarymovement being that which causes dial 37 to rotate about its own axis,it is thus seen that a reduced lmovement thereof is secured.

The arrangement of Fig. 2 is of course applicable to other types ofcondenser, in which a large shaft movement is necessary to produce afull movement of the variable condenser.

In this figure I also show a toroidal astatic inductancc coil 58, whichcan be used in I illustrate a conjunction with the condenser, to formIa. complete tuning unit. There is ample space for this coil in the covermember 33, and it can be arranged to be coaxial with the condenserelectrodes. In order to permit the carrying out of this compactarrangement, merely a binding post 59 is provided in lieu of the spring30,' and furthermore, several projections can be provided in covermember 33 between which the coil can be readily sprung. to retain it inplace.

In many sets now on the market, it is possible to tune accuratelyseveral stages of radio frequency by the movement of a common shaft. Mycondenser structure is especially adapted for this type of set. Iillustrate in Fig. 3 one embodiment of a multiple condenser constructedin accordance with m invention. In this figure a hollow tube 45 ofinsulating material carries within it, a series of stationary electrodestructures 46, the extreme left hand structure serving as a closure forthat end of the tube. A cover 47 may be provided in the other end whichalso serves to support the long shaft 48, extending thru the entirestructure. This shaft is journaled in the stationary electrodes 46 andadjustably carries a plurality of worms 49. The` adjustment of theseworms may be performed by the aid of set screws 50, which serve to holdthe worms 49 to the shaft 48. The movable electrodes 51 are providedwith threaded portions 52 engaged by the Worms 49, whereby upon rotationof shaft 48 all of the movable electrode structures 51 are axiallymoved.

The connection foreach of the condenser elements may he provided asindicated and in general are substantially identical to that illustratedin Fig. 1.

Since each of the worms 49 may be ndependently adjusted along the axisby the aid of their set screws 50. it is possible to compensate for lackof uniformity in the radio frequency circuits which are to be tunedSimultaneously by this structure. In other rrespects, the operation ofthe condensers is substantially identical with that already disclosed. Ialso indicate a toroidal inductance coil 58 in this embodiment,- to forma timing unit with at least one of the condensers. In this instance, thecoil is shown as supported by the aid of several saddles 61 fastened tothe inside of tube 45.

lt is possible to cause relative movement of the electrode structure bymechanism other than the worm and nut arrangement thus far disclosed. Asan additional example of such' plurality of other forms, I show in Fig.4 an arrangement whereby a roller 53 is fastened to the operating shaft54 of the condenser. and.is arranged to co-act with a cam surface 55 atthe right hand surface of the hub 56. formed on the movable electrode.structure 57. This cam surface 44 may conj of faid electrode,

venientl be in the form of helicoid of steep pitch. fh this way, acomplete rotation of the dial 12 can cause a complete movement of themovableelectrode 57 on the hub extension 16. The spring 30 serves tocause a proper engagement at all times between the cam roller 53 and thecam surface 55. The` electrode 57 is of course limited in its movementby the walls of he enclosing casing.

I claim:

1. In a variable condenser, a pair of electrodes, one of said electrodeshaving a ringlike body forming said electrode, on which there' is anannular inner active surface, said body having one end closed, aninsulating closure for the other end, and means for supporting the otherelectrode in the space enclosed by the body and the closure, in suchmanner as to permit relative movement of the electrodes.

2. In a variable condenser, a stationary electrode, a movable electrode,a rotatable shaft, a screw on the shaft for moving said movableelectrode, and means for axially adjusting said screw with respect tothe shaft.

3. In a variable condenser, a stationary, hollow electrode having aninner active surface extending around an axis of symmetry said electrodealso having a hub at the axis. a shaft journaled in said hub forrotation about said axis, an electrode structure movable axially of theshaft, and slidable along said hub, said electrode structure having anouter surface cooperating with the said inner surface of the stationaryelectrode, a worm pn said shaft engaging threads in the said movableelectro-de structure to move it axially, an insulating cover fastened tothe stationary electrode and enclosing the movable electrode, a bindingpost extending through said cover, and a metallic spring member fastenedat one end to the inner end of the binding post, and fastened at theother end to the movable electrode structure and serving to provide aconnection therefor.

4. In combination, a tubular' insulation member, a series of spaced,annular stationarg electrodes fastened within the hollow tu ular member,a shaft extending through the tubular member and through the stationaryelectrodes, and a series of movable electrodes carried by the shaft andcooperating with the stationary electrodes.

In testimony whereof I have hereunto set my hand.

HAROLD F. ELLIOTT.

